One-piece, lightweight, disposable drinking cups molded from expanded or expandable beads of polystyrene have gained great favor in recent years for the service of coffee and other hot beverages because of their low cost and good thermal insulating characteristics. However, because it is necessary to maintain the spacing between the opposed mold surfaces in the molding equipment of the types commonly used to make such cups at some substantial multiple of the average size of the commercially available types of expanded or expandable beads from which such cups are molded, in order to get such beads to properly fill the molds, such cups are characterized by thick sidewalls, relative to other types of hot drink cups. Thus, because of the sidewall thickness characteristics of such cups, they cannot be nested within one another as closely together in stacks as other types of hot drink cups, and such cups, therefore, occupy considerably more space in shipment and storage than other hot drink cups. This fact has greatly limited the use of such cups in the sale of coffee from vending machines.
It has previously been proposed, in Belgium Pat. No. 777,675, that cups molded from expanded beads of polystyrene can be formed with a thinner section near the top or rim of each such cup, and which would, therefore, be near the bottom of the top-charged types of molding equipment conventionally used in molding cups from expandable beads in the inverted position. However, the reduction in stacking height which can be achieved by the use of the configuration of the aforesaid Belgium Patent is limited by the minimum sidewall thickness required near the bottom of such cups, which is somewhat greater than the thickness required at the top thereof.